A retrorocket is a rocket engine used to provide thrust opposing the motion of a spacecraft, thereby causing it to decelerate. When a spacecraft in orbit is slowed sufficiently, its altitude decreases to the point at which aerodynamic forces begin to rapidly slow the motion of the vehicle, and it returns to the ground. Without such rockets, spacecraft would remain in orbit for years until their orbits naturally slow, and reenter the atmosphere at a much later date; in the case of manned flights, long after life support systems have been expended. Therefore it is critical that spacecraft have extremely reliable retrorockets. A Soyuz rocket, at Baikonur launch pad. ... An engine in the broadest sense, is something that produces an output effect from a given input. ... Thrust is a reaction force described quantitatively by Newtons Second and Third Laws. ... The Space Shuttle Discovery as seen from the International Space Station. ... Two bodies with a slight difference in mass orbiting around a common barycenter. ... Atmospheric entry is the transition from the vacuum of space to the atmosphere of any planet or other celestial body. ...

One of the first uses of retrorocket technology was in the Hajile project initiated by the British Admiralty's Directorate of Miscellaneous Weapons Development. Originally a request from the British Army as a method to drop heavy equipment or vehicles from aircraft flying at high speeds and altitudes, the project turned out to be a huge disaster and was forgotten after World War II. Although some of the tests turned out to be successful, Hajile was too unpredictable to be used in conventional warfare, and by the time the war drew to a close, with no chance to put the project into action, it was shelved. Hajile was one of a number of highly experimental projects, including the Hedgehog and Panjandrum, that were developed by the British Admiraltys Directorate of Miscellaneous Weapons Development (DMWD) during the final years of World War II. The project was initiated by a request from the Army for a method... Combatants Allied powers: China France Great Britain Soviet Union United States and others Axis powers: Germany Italy Japan and others Commanders Chiang Kai-shek Charles de Gaulle Winston Churchill Joseph Stalin Franklin Roosevelt Adolf Hitler Benito Mussolini Hideki Tōjō Casualties Military dead: 17,000,000 Civilian dead: 33,000...

Due to the high reliability demanded by retrorockets, Mercury spacecraft used a trio of solid fuel, 1000 lbf (4.5 kN) thrust retrorockets strapped to the heat shield on the bottom of the spacecraft that fired for 10 seconds each. One was sufficient to return the spacecraft to earth if the other two failed. Gemini used a similar system as Mercury, just scaled up to four rockets of 2500 lbf each (11 kN) that burned for 5.5 seconds each. These rockets were part of the Reentry Control System mounted forward of the pressurized cabin. Mercury program monument Project Mercury was the United States first manned spaceflight program. ... The pound-force is a non-SI unit of force or weight (properly abbreviated lbf or lbf). The pound-force is equal to a mass of one pound multiplied by the standard acceleration due to gravity on Earth (which is defined as exactly 9. ... The newton (symbol: N) is the SI unit of force. ... Project Gemini was the second human spaceflight program of the United States of America. ...

Project Apollo did not require retrorockets for lunar flights, as the flight from the moon was directed to fly the spacecraft directly back to earth, and not enter orbit. However, the flights in earth orbit for tests required retrorockets, so the large, versatile Service Propulsion Module on the Service Module was used to decelerate the spacecraft. The Space Shuttle would use a similar multipurpose engine for reentry. Project Apollo was a series of human spaceflight missions undertaken by the United States of America (NASA) using the Apollo spacecraft and Saturn launch vehicle, conducted during the years 1961 – 1975. ... NASAs Space Shuttle, officially called Space Transportation System (STS), is the United States governments current manned launch vehicle. ...

The Space Shuttle Orbital maneuvering system provides the vehicle with a pair of powerful liquid fueled rockets for both reentry and orbital maneuvering. One is sufficient for a successful reentry, and if both systems should fail, the Reaction control system can slow the vehicle enough for reentry. An OMS pod detached from a Shuttle for maintenance. ... A reaction control system (abbreviated RCS) is a subsystem of a spacecraft. ...

Retrorockets are also used in landing spacecraft on other astronomical bodies, such as the Moon and Mars, as well as enabling a spacecraft to enter an orbit encircling such a body, when otherwise it would scoot past and off into space again. As pointed out above (in connection with Project Apollo) the main rocket on a spacecraft can be re-oriented to serve as a retrorocket. Apparent magnitude: up to -12. ... Adjectives: Martian Atmosphere Surface pressure: 0. ... Project Apollo was a series of human spaceflight missions undertaken by the United States of America (NASA) using the Apollo spacecraft and Saturn launch vehicle, conducted during the years 1961 – 1975. ...